Computer networks have become ubiquitous. Computer networks include the Internet, Service Provider (SP) networks, private networks, and Local Area Networks (LANs). A network such as an SP network may include peripherally located Provider Edge (PE) routers, each of which couples to one or multiple Customer Edge (CE) routers. The PE routers are used to maintain routing and forwarding context for each customer. The CE routers may couple to private LANs associated with one or multiple customers. The private LANs are frequently referred to as core networks. The PE routers learn local customer routes from the CE routers and distribute remote customer routes to the CE router. The PEs may use Border Gateway Protocol (BGP) to distribute customer routes to each other.
To support operation, the PE routers typically maintain Virtual Routing and Forwarding (VRF) information in a table (a VRF table) dictating how to route and forward traffic through the shared physical network to support corresponding Virtual Private Networks (VPNs) for the different customers. Typically, the SP network selectively couples the LANs to each other through links created between its PE routers. For the core network, an ingress PE may use BGP functions to determine the egress PE. The ingress PE can put the packet in a two-level Multi Protocol Label Switching (MPLS) stack. The top label is used to tunnel packets to the egress PE to accomplish MPLS forwarding through the core network. The bottom label is used by the egress PE to identify the outgoing route for the packet. VPNs provide a secured means for transmitting and receiving data between network nodes even though a corresponding physical network supporting propagation of the data is shared by many users (and VPNs). In a typical networking environment used for routing data, the environment may include a number of Customer Edge (CE) routers, a number of Provider Edge (PE) routers and a packet-switched network (PSN). Data, encapsulated in layer-2 frames, may be forwarded from a first CE router to a first PE router, from the first PE router across the PSN to a second PE router, and from the second PE router to a second CE router.
In particular conventional systems, a PDU (e.g., a frame) traverses the networking environment beginning at a first CE router and ending up at a second CE router. The first CE router sends a layer-2 PDU to an ingress PE router. The ingress PE router receives the PDU and encapsulates the PDU with MPLS labels which are used to identify the individual port/circuit and the egress layer-3 PE router. The encapsulated PDU is then forwarded on the PW, across the packet-switched network, to an egress layer-3 PE router. The egress layer-3 PE router removes the MPLS label that identifies the port/circuit that was added by the ingress PE router and forwards the layer-2 PDU to the second CE router.
Pseudowires (“PWs”) are known in the art of computer networking and telecommunications. A Pseudowire (PW) may be utilized to transfer data across the PSN. In general, a pseudowire is an emulation of the essential attributes of a telecommunications service over a Packet Switched Network (“PSN”). The service may be ATM, T1 leased line, Frame Relay, Ethernet, low-rate TDM, or SONET/SDH, for example. The PSN may be Multiprotocol Label Switching (“MPLS”), IP (either Ipv4 or Ipv6), or Layer 2 Tunnel Protocol Version 3 (“L2TPv3”). The functions provided by a PW includes encapsulating service-specific bit streams, cells, or PDUs arriving at an ingress port and carrying them across a path or tunnel, managing their timing and order, and any other operations required to emulate the behavior and characteristics of the particular service. Pseudowires can be used to carry ingress layer-2 traffic from an ingress PE router to an egress PE router, and the forward the layer-2 traffic out of an egress port of the egress PE router.
Multi-Segment Pseudowires (“MS-PWs”) are also known in the art. MS-PWs may transit more than one PSN domain and more than one PSN tunnel. MS-PWs have become necessary for the extension of network and transport services such as layer-2 and layer-3 technologies across domains. A domain refers to a collection of network elements within a common sphere of address management or path computational responsibility such as an IGP area, Autonomous System (“AS”), service provider area, or area with reduced routing state such as is the case with Route Summarization in effect. Multiple pseudowire segments (i.e., single-hop pseudowires) are stitched together to create a single end-to-end multi-segment pseudowire (i.e., a multi-hop pseudowire) from the source of the pseudowire to the destination of the pseudowire.